Fix minor typo in stamp.bzl (#559)

Co-authored-by: Alex Eagle <eagle@post.harvard.edu>

python/private/stamp.bzl

diff --git a/python/private/stamp.bzl b/python/private/stamp.bzl
index 86ea3fc..6d0e549 100644
--- a/python/private/stamp.bzl
+++ b/python/private/stamp.bzl
@@ -53,7 +53,7 @@
     )
 
 def is_stamping_enabled(attr):
-    """Determine whether or not build staming is enabled
+    """Determine whether or not build stamping is enabled
 
     Args:
         attr (struct): A rule's struct of attributes (`ctx.attr`)